Lalit bhati ppt osi

OutlineOutline

THE OSI MODELTHE OSI MODEL HISTORYHISTORY WHY DO WE NEED OSI MODALWHY DO WE NEED OSI MODAL WORKS OF DIFFERENT LAYERSWORKS OF DIFFERENT LAYERS LAYERS AND PROTOCOLSLAYERS AND PROTOCOLS COMMUNICATION BETWEEN CLIENTCOMMUNICATION BETWEEN CLIENT SUMMARY SUMMARY

The OSI Model The OSI Model

HISTORYHISTORY

The The OSI Reference Model OSI Reference Model was a major was a major advance in the teaching of network advance in the teaching of network concepts. It promoted the idea of a concepts. It promoted the idea of a consistent model of protocol layers, consistent model of protocol layers, defining interoperability between defining interoperability between network devices and software. The network devices and software. The OSI model was established by ISO in OSI model was established by ISO in 1984.1984.

Why do we need OSI ModelWhy do we need OSI Model

Over the past couple of decades many of the networks that Over the past couple of decades many of the networks that were built used different hardware and software were built used different hardware and software implementations, as a result they were incompatible and it implementations, as a result they were incompatible and it became difficult for networks using different specifications to became difficult for networks using different specifications to communicate with each other. communicate with each other.

To address the problem of networks being incompatible and To address the problem of networks being incompatible and unable to communicate with each other, the International unable to communicate with each other, the International Organisation for Standardisation (ISO) researched various Organisation for Standardisation (ISO) researched various network schemes. network schemes.

The ISO recognised there was a need to create a NETWORK The ISO recognised there was a need to create a NETWORK MODEL that would help vendors create interoperable network MODEL that would help vendors create interoperable network implementations.implementations.

The OSI Reference Model is composed of seven The OSI Reference Model is composed of seven layers, each specifying particular network layers, each specifying particular network functions.functions.The process of breaking up the functions or The process of breaking up the functions or tasks of networking into layers reduces tasks of networking into layers reduces complexity.complexity.Each layer provides a service to the layer above Each layer provides a service to the layer above it in the protocol specification.it in the protocol specification. Each layer communicates with the same layer’s Each layer communicates with the same layer’s software or hardware on other computers. software or hardware on other computers.

Why do we need OSI Model

The lower 4 layers (transport, network, data link The lower 4 layers (transport, network, data link and physical —Layers 4, 3, 2, and 1) are and physical —Layers 4, 3, 2, and 1) are concerned with the flow of data from end to end concerned with the flow of data from end to end through the network. through the network. The upper four layers of the OSI model The upper four layers of the OSI model (application, presentation and session—Layers (application, presentation and session—Layers 7, 6 and 5) are orientated more toward services 7, 6 and 5) are orientated more toward services to the applications. to the applications. Data is Data is Encapsulated with the necessary Encapsulated with the necessary protocol information as it moves down the layers protocol information as it moves down the layers before network transit.before network transit.

WORKS OF DIFFERENT LAYERS

Physical LayerPhysical Layer

The physical layer deals with the physical The physical layer deals with the physical characteristics of the transmission medium.characteristics of the transmission medium.

It defines the electrical, mechanical, procedural, It defines the electrical, mechanical, procedural, and functional specifications for activating, and functional specifications for activating, maintaining, and deactivating the physical link maintaining, and deactivating the physical link between end systems. between end systems.

Physical LayerPhysical Layer

Such characteristics as voltage levels, timing of voltage Such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission changes, physical data rates, maximum transmission distances, physical connectors, and other similar distances, physical connectors, and other similar attributes are defined by physical layer specifications. attributes are defined by physical layer specifications.

Examples :- EIA/TIA-232, RJ45, NRZ.Examples :- EIA/TIA-232, RJ45, NRZ.

Data Link LayerData Link Layer

The data link layer provides access to the networking The data link layer provides access to the networking media and physical transmission across the media and media and physical transmission across the media and this enables the data to locate its intended destination on this enables the data to locate its intended destination on a network.a network.

The data link layer provides reliable transit of data The data link layer provides reliable transit of data across a physical link by using the Media Access Control across a physical link by using the Media Access Control (MAC) addresses.(MAC) addresses.

Data Link Layer Sub layersData Link Layer Sub layers

LLC LLC Upper sub layerUpper sub layer Provides common interfaceProvides common interface Supplies reliability and flow control servicesSupplies reliability and flow control services

MACMAC Lower sub layerLower sub layer Appends physical address of destination Appends physical address of destination

computer onto the framecomputer onto the frame

Data Link LayerData Link Layer

The data link layer uses the MAC address to define a The data link layer uses the MAC address to define a hardware or data link address in order for multiple hardware or data link address in order for multiple stations to share the same medium and still uniquely stations to share the same medium and still uniquely identify each other.identify each other.

Concerned with network topology, network access, error Concerned with network topology, network access, error notification, ordered delivery of frames, and flow control.notification, ordered delivery of frames, and flow control.

Examples :- Ethernet, Frame Relay, FDDI.Examples :- Ethernet, Frame Relay, FDDI.

FramesFrames

Structured package for moving dataStructured package for moving dataIncludes raw data (or payload) along with sender’s and Includes raw data (or payload) along with sender’s and receiver’s:receiver’s:

Network addressesNetwork addresses Error-checking and control informationError-checking and control information

Figure 2-2: A simplified data frame

Network LayerNetwork Layer

Third layer of OSI ModelThird layer of OSI Model

Translates network addresses into their Translates network addresses into their physical counterpartsphysical counterparts

Decides how to route data from sender to Decides how to route data from sender to receiverreceiver

Network LayerNetwork Layer

Because Network layer handles routing, Because Network layer handles routing, routersrouters belong in Network layer belong in Network layer To To routeroute means to direct data based on means to direct data based on

addressing, usage patterns, and availabilityaddressing, usage patterns, and availability

Network layer protocols also accomplish:Network layer protocols also accomplish: SegmentationSegmentation ReassemblyReassembly

Examples :- IP, IPX, AppleTalk.Examples :- IP, IPX, AppleTalk.

Transport LayerTransport Layer

Fourth layer of OSI ModelFourth layer of OSI Model

Ensures that data are transferred between Ensures that data are transferred between points reliably and without errorspoints reliably and without errors

Handles Handles flow controlflow control Method of gauging appropriate rate of data Method of gauging appropriate rate of data

transmissiontransmission

Transport LayerTransport Layer

SequencingSequencing Process of assigning a placeholder to each piece Process of assigning a placeholder to each piece

of a data block to allowing receiving node’s of a data block to allowing receiving node’s Transport layer to reassemble data in correct Transport layer to reassemble data in correct orderorder

Acknowledgement (ACK)Acknowledgement (ACK) Response generated in Transport layerResponse generated in Transport layer Confirms to sender that its frame was receivedConfirms to sender that its frame was receivedLayer 4 protocols include TCP (Transmission Layer 4 protocols include TCP (Transmission Control Protocol) and UDP (User Datagram Control Protocol) and UDP (User Datagram Protocol).Protocol).

Session LayerSession Layer

The session layer defines how to start, The session layer defines how to start, control and end conversations (called control and end conversations (called sessions) between applications.sessions) between applications.This includes the control and management This includes the control and management of multiple bi-directional messages using of multiple bi-directional messages using dialogue control.dialogue control.It also synchronizes dialogue between two It also synchronizes dialogue between two hosts' presentation layers and manages hosts' presentation layers and manages their data exchange.their data exchange.

Session LayerSession Layer

The session layer offers provisions for The session layer offers provisions for efficient data transfer.efficient data transfer.

Examples :- SQL, ASP (AppleTalk Examples :- SQL, ASP (AppleTalk Session Protocol).Session Protocol).

Presentation LayerPresentation Layer

The presentation layer ensures that the information The presentation layer ensures that the information that the application layer of one system sends out is that the application layer of one system sends out is readable by the application layer of another system.readable by the application layer of another system. If necessary, the presentation layer translates If necessary, the presentation layer translates between multiple data formats by using a common between multiple data formats by using a common format. format.

Provides encryption and compression of data.Provides encryption and compression of data.Examples :- JPEG, MPEG, ASCII, EBCDIC, HTML.Examples :- JPEG, MPEG, ASCII, EBCDIC, HTML.

Application LayerApplication Layer

The application layer is the OSI layer that The application layer is the OSI layer that is closest to the user.is closest to the user.

It provides network services to the user’s It provides network services to the user’s applications. applications.

It differs from the other layers in that it It differs from the other layers in that it does not provide services to any other OSI does not provide services to any other OSI layer, but rather, only to applications layer, but rather, only to applications outside the OSI model. outside the OSI model.

Application LayerApplication Layer

Examples of such applications are Examples of such applications are spreadsheet programs, word processing spreadsheet programs, word processing programs, and bank terminal programs. programs, and bank terminal programs.

The application layer establishes the The application layer establishes the availability of intended communication availability of intended communication partners, synchronizes and establishes partners, synchronizes and establishes agreement on procedures for error agreement on procedures for error recovery and control of data integrity.recovery and control of data integrity.

Layers and Protocols

Communication Between Sender Communication Between Sender and Receiver and Receiver

How Data transfer

between two systems

Communication Between Sender Communication Between Sender and Receiverand Receiver

Data transformed through the OSI Model

SummarySummary

Standards are documented agreements containing Standards are documented agreements containing technical specifications or other precise criteria technical specifications or other precise criteria used as guidelines to ensure materials, products, used as guidelines to ensure materials, products, processes, and services suit their purposeprocesses, and services suit their purpose

Prominent standards organization include:Prominent standards organization include: ANSIANSI EIAEIA IEEEIEEE ISOISO ITUITU

SummarySummary

OSI Model divides networking architecture OSI Model divides networking architecture into seven layers:into seven layers: Physical layerPhysical layer Data Link layerData Link layer Network layerNetwork layer Transport layerTransport layer Session layerSession layer Presentation layerPresentation layer Application layerApplication layer

SummarySummary

A data request from a software program is received A data request from a software program is received by Application layer services and is transferred by Application layer services and is transferred down through layers of OSI Model until it reaches down through layers of OSI Model until it reaches the Physical layerthe Physical layer

Data frames are small blocks of data with control, Data frames are small blocks of data with control, addressing, and handling information attached to addressing, and handling information attached to themthem

Each node on a network can be identified by two Each node on a network can be identified by two types of addresses:types of addresses: Network layer addressNetwork layer address Data Link layer addressData Link layer address

SummarySummary

In addition to frame types, IEEE networking In addition to frame types, IEEE networking specifications apply to connectivity, specifications apply to connectivity, networking media, error checking algorithms, networking media, error checking algorithms, encryption, emerging technologies, and moreencryption, emerging technologies, and more

ISO expanded OSI Model by separating the ISO expanded OSI Model by separating the Data Link layer into sublayers:Data Link layer into sublayers: LLC layerLLC layer MAC layerMAC layer

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